Why can I only hire *LESS* powerful Mercenaries?

This is something that really just makes zero sense to me. If I'm having problems on a board, why would I plunk down almost 20 thousand gold to hire someone less powerful than the characters I already have?
Or maybe, if I'm super lucky and every one of my guildmates will be the same level as me all the time, they'll be the same power as me.

This still makes zero sense.

I am currently stuck on the Elite Swordmaster. My level 49 team gets 1-shotted by him constantly. Today I got all 5 of my heroes to him with full energy and 100% health. They all still died when Swordmaster did his ultimate.

Now, why would I waste 20k gold to make an attempt with someone weaker? I should be able to plunk down some gold to try the mission with someone 5 levels higher than me. If I'm in a guild with higher level guys, I should be able to give them some money to help me out. But currently, since I'm level 49, there is nothing I can do to help a level 50, 52, or 53 level guy. I can get a level 54 guy 1000 gold through worship, but I should also be able to hire his Shadow or Panda to see if I like it and get by those quests I'm having difficulties with.

This is something that really just makes zero sense to me. If I'm having problems on a board, why would I plunk down almost 20 thousand gold to hire someone less powerful than the characters I already have?
Or maybe, if I'm super lucky and every one of my guildmates will be the same level as me all the time, they'll be the same power as me.

This still makes zero sense.

I am currently stuck on the Elite Swordmaster. My level 49 team gets 1-shotted by him constantly. Today I got all 5 of my heroes to him with full energy and 100% health. They all still died when Swordmaster did his ultimate.

Now, why would I waste 20k gold to make an attempt with someone weaker? I should be able to plunk down some gold to try the mission with someone 5 levels higher than me. If I'm in a guild with higher level guys, I should be able to give them some money to help me out. But currently, since I'm level 49, there is nothing I can do to help a level 50, 52, or 53 level guy. I can get a level 54 guy 1000 gold through worship, but I should also be able to hire his Shadow or Panda to see if I like it and get by those quests I'm having difficulties with.